X-Git-Url: https://gerrit.fd.io/r/gitweb?a=blobdiff_plain;f=doc%2Fguides%2Fprog_guide%2Fmetrics_lib.rst;h=e68e4e7431aeff466b9c1c64556d20515d510655;hb=a4712f588e6e7f556698eea7fbc2514d175693a6;hp=5cbe17c9037a41ef62c8b67bf0fa8b2da61ce4b7;hpb=8a853e3f0275efc8b05cb195085d45946942744a;p=deb_dpdk.git

diff --git a/doc/guides/prog_guide/metrics_lib.rst b/doc/guides/prog_guide/metrics_lib.rst
index 5cbe17c9..e68e4e74 100644
--- a/doc/guides/prog_guide/metrics_lib.rst
+++ b/doc/guides/prog_guide/metrics_lib.rst
@@ -271,3 +271,12 @@ de-initialise the latency library.
 .. code-block:: c
 
     rte_latencystats_uninit();
+
+Timestamp and latency calculation
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The Latency stats library marks the time in the timestamp field of the
+mbuf for the ingress packets and sets the ``PKT_RX_TIMESTAMP`` flag of
+``ol_flags`` for the mbuf to indicate the marked time as a valid one.
+At the egress, the mbufs with the flag set are considered having valid
+timestamp and are used for the latency calculation.